This invention relates to a method of assembling electron guns for cathode-ray tubes and, more particularly, to a method of assembling an electron gun comprising a step of accurately welding strap conductors to predetermined positions of an electron gun having a number of electrodes by using a laser beam.
Usually, with an electron gun for a cathode-ray tube, which has a comparatively simple electrode construction, for instance an ordinary bi-potential type electron gun having first to fourth grids, voltages are applied to the first to fourth grids through strap conductors. The connection of grid and strap conductor in this case is made by clamping the strap conductor in a lug provided on the grid and welding it by resistance welding.
However, at the time of the resistance welding of the grid and strap conductor to each other, splash takes place, and metal powder is attached to the grid surface to deteriorate the breakdown characteristics of the electron gun. In addition, deformation of the grid is liable to be caused by pressure application at the time of welding. Further, the effective diameter of the electron gun is reduced by the presence of the lug which is provided on the grid for the purpose of welding.
The aforementioned disadvantages in the case of adopting the resistance welding are particularly pronounced when assembling an electron gun having a complicated electrode construction having many positions where strap conductors are welded, as shown in FIGS. 1 to 3.
The electron gun shown in FIGS. 1 to 3 comprises a cathode 1 containing a heater (not shown), a first grid 2, a second grid 3, a third grid 4, a fourth grid 5, a fifth grid 6, a sixth grid 7 and a convergence electrode (not shown). The first grid 2 is a cup-shaped electrode, the second grid 3 is a plate electrode, the third electrode 4 consists of two cup-shaped electrodes 4a and 4b, the fourth grid 5 consists of three plate electrodes 5a, 5b and 5c, the fifth grid 6 consists of four electrodes, namely a cup-shaped electrode 6a, a plate electrode 6b and two cup-shaped electrodes 6c and 6d stacked in the mentioned order, and the sixth grid 7 consists of two cup-shaped electrodes 7a and 7b. The cathode 1 and first to sixth grids 2 to 7 are supported at predetermined spacings by insulating support members 8 such as bead glass. Reference numeral 9 designates a support plate for supporting the heater and securing the electron gun on the stem.
With the electron gun of the above construction, a voltage of about 25 KV is applied through a strap conductor R-1, a convergence electrode (not shown) and a bulb spacer (not shown) to the sixth grid 7, a voltage of about 7 KV through a strap conductor R-2 to the fifth and third grids 6 and 4, a voltage of several hundred volts through a strap conductor R-3 to the fourth and second grids 5 and 3, and earth voltage through a strap conductor R-4 to the first grid 2.
With the above electron gun having a complicated electrode construction, the number of strap conductors electrically connecting grids is greater than the case of the electron gun having a simpler electrode construction, and hence there are a greater number of points of connection of these strap conductors to the grids; namely the strap conductor R-1 has two junctures on the cup-shaped electrodes 7a and 7b, the strap conductor R-2 has a total of six junctures, four on the cup-shaped electrodes 6a, 6c and 6d and the plate electrode 6b and two on the cup-shaped electrodes 4a and 4b, the strap conductor R-3 has a total of four junctures, three on the plate electrodes 5a, 5b and 5c and one on the second grid 3, and the strap conductor R-4 has one juncture on the first grid 2. Connecting the individual strap conductors to a number of peripheral edge portions of the electrodes as mentioned above by resistance welding involves technical difficulties and requires much time if it could be made. Therefore, the conventional welding method does not only require high cost but also imposes restrictions upon the quantity of production.